In 2000, seven cases of clinical islet transplantation were reported from University of Alberta in Edmonton, Canada(Shapiro A M, Lakey J R, Ryan E A, et al., N Engl J Med 343:230-238, 2000). The report was that by a novel method for using immunosuppressant which was called “Edmonton Protocol” later, all the cases with type I diabetes who underwent pancreatic islet transplantation became free from daily administration of insulin. At the present time, pancreatic islet transplantation is the closest to an ideal curing method for patients with insulin-dependent diabetes mellitus.
Pancreas under retroperitoneum is composed of exocrine gland and endocrine glands. Exocrine gland accounts for at least 98% of the whole pancreas volume, whereas endocrine glands account for at most 2%. Endocrine tissue which was found by Langerhans in 1869 is called pancreatic islet. Pancreatic islet is an aggregate of endocrine cells, and comprises a cells, β cells, PP cells and δ cells and the like. Insulin is secreted by β cells in pancreatic islets, said insulin being the only endogenous hormone which has the effect of decreasing blood sugar. The aim of pancreatic islet transplantation is to replace a system for decreasing blood sugar, said system which has declined, and regenerate one by separating pancreatic islets from pancreas and transplanting them to a patient who suffers from insulin-dependent diabetes mellitus.
Whether or not pancreatic islets are successfully separated depends on the quality of pancreas itself used for the separation. In addition, in order to successfully separate pancreatic islets, it is necessary that exocrine gland tissue should be in a good condition. Tact beyond expectation is required in the case where pancreas is taken for the purpose of separating pancreatic islets. If pressure is only applied to pancreas by touching the pancreas, for example, the pancreatic exocrine cells release proteases which these cells contain, followed by autocytolysis. In the case pancreas is separated at a distant place, it is necessary that the pancreas should be preserved with great caution during the transport of it to facilities for the separation of the cells.
Based on the cause of decline in insulin activity, diabetes is generally classified into type I diabetes (juvenile-onset diabetes) and type II diabetes. Because the control of blood sugar by insulin treatment is extremely difficult in the case of type I diabetes in which insulin is little secreted compared with the case of type II diabetes in which the secretion of insulin is maintained within a certain extent, pancreatic islet transplantation is considered as the most effective treatment. Also in type II diabetes, insulin shortage is caused by glucose toxicity or β-cell fatigue if the stage progresses. However, pancreatic islet transplantation has not been indicated for type II diabetes. The reason is that there is insulin resistance in a basic condition of type II diabetes, whereby it is worried whether or pancreatic islet transplantation is effective. Although the exact control of blood sugar leads a good convalescence in type II diabetes, the case of type I diabetes alone is the subject of pancreatic islet transplantation on the basis of the real fact that pancreatic islets for transplantation is in short supply. In the future if comes the situation where a great number of pancreatic islets for transplantation can be supplied, there is a great possibility that pancreatic islet transplantation is indicated for insulin dependent diabetes mellitus with insulin resistance.
At the time when insulin treatment was developed, it was believed that type I diabetes became a completely controllable disease by insulin treatment. However, it was found that insulin treatment caused a long-term complication such as retinopathy, neuropathy or nephropathy, and that type I diabetes brought patients other suffering in the form of a chronic disease. Insulin treatment plays a key role in solving the emergency problem of a prompt death in type I diabetes, and in the point that insulin treatment can be offered to any patient at the present time. However, insulin treatment can not be a method for treating type I diabetes completely, an extremely difficult problem such as the risk of hypoglycemia or long-term complications persists.
Type I diabetes is caused by autoimmune abnormalities in which pancreatic β cells secreting insulin are specifically destroyed (Atkinson Mass., Maclaren N K., N Engl J Med 331:1428-1436,1994). To completely treat type I diabetes, transplantation which is one of the treatments for regenerating and substituting for pancreatic p cells is considered. As a transplantation, there are a pancreas transplantation and a pancreatic islet transplantation. The purposes of these two kinds of transplantation is to enable the extremely exact control of blood sugar, and to prevent hypoglycemia and a long-term complication from being caused. It is not the only purpose to release patients from daily bother in insulin treatment and then improve the quality of life (QOL). As a measure to achieve the goal of completely curing insulin-dependent diabetes mellitus, transplantation therapies have much greater possibilities than insulin treatment does. In pancreas transplantation, however, there are problems that an operative risk is serious, and that the complications caused by a concomitantly transplanted exocrine gland can be severe. In the case of pancreatic islet transplantation, there is a problem of safety caused by using immunosuppressant. Another problem is that much smaller is the number of pancreases taken from neomorts necessary for the separation of pancreas/pancreatic islets, compared with the number of patients in need thereof, and consequently there is no probability that the situation will be overcome.
As a source of cells which substitute for human mature pancreatic β cells, human ES cells and tissue stem cells, for example, are being intensively studied at the present time. Although it was reported that insulin expression was observed after induction of differentiation in the case of some kinds of cells (murine ES cells and hepatic stem cells), it is still unclear which gene(s) should be introduced at which stage for effective insulin secretion. In addition, the use of such stem cells essentially involves difficulties in control, said difficulties arising from the fact that these stem cells have pluripotency and active proliferation potency. It is considered that plenty of time is necessary to put these cells to practical use in the future.
Study using porcine tissues/cells progresses, whereas these problems of xenozoonosis, tissue compatibility and ethics have surfaced. In special, potential risks connected with virus have become a big problem. Risks that virus which porcine organs or cells contain infects a recipient thereby causing a disease (it is especially impossible to remove porcine endogenous retrovirus (PERV), because PERV is integrated in chromosome) include the risk, for example, that the infection spreads to the family and medical staff, and consequently new virus infection spreads in the world.
At the present time, therefore, deeply desired is a source of cells which is preferable in quality and amount (quantity), and substitutes for human mature pancreatic β cells.
An object of the present invention is to solve conventional problems, and to provide a cell line which can express insulin in a glucose-concentration dependent manner, and enables the easy obtainment of the number of cells, said number which meets the demand. Another object is to provide a therapeutical cell preparation for diabetes treatment.